Hydraulic control system for automatic transmission

ABSTRACT

A hydraulic control system for a fluid controlled automatic transmission having means for controlling fluid pressure applied to servo chambers for multiple disc clutch means and brake band means for carrying out an automatic speed change. In the system, the fluid pressure is varied depending on the load on the engine represented by a variable such as the negative pressure in the air intake manifold or the opening of the engine throttle valve.

United States Patent Ito et al.

[54] HYDRAULIC CONTROL SYSTEM FOR AUTOMATIC TRANSMISSION [72] inventors:Shin Ito; Seitoku Kubo; Takakazu Mori, all of Toyota, Japan [73]Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota-shi, Japan [22]Filed: Dec. 15, 1970 211 Appl.No.: 98,271

[30] Foreign Application Priority Data Dec. 16, 1969 Japan ..44/101441[52] US. Cl ..74/866 [51] Int. Cl. ..B60k 21/00 [58] Field of Search..74/866 [56] References Cited UNITED STATES PATENTS 3,433,101 3/l969Scholl et al. 74/ 8 66 [451 Oct.31,l972

Pfisterer et al. ..74/866 Nelson ..74/866 Primary Examiner-C. J. I-lusarAttorney-Cushman, Darby & Cushman [5 7 ABSTRACT A hydraulic controlsystem for a fluid controlled automatic transmission having means forcontrolling fluid pressure applied to servo chambers for multiple discclutch means and brake band means for carrying out an automatic speedchange. In the system, the fluid pressure is varied depending on theload on the engine represented by a variable such as the negativepressure in the air intake manifold or the opening of the enginethrottle valve.

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/ IIIH HNIIIJIII INVENTORS BYW JZI 'M ATTORNEYS HYDRAULIC CONTROL SYSTEMFOR AUTOMATIC TRANSMISSION BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to hydraulic control systems for fluidcontrolled automatic transmissions having means for controlling fluidpressure or line pressure P applied to servo chambers for multiple discclutch means and brake band means for carrying out an automatic speedchange, and more particularly to a hydraulic control system of the kinddescribed above in which the fluid pressure is varied depending on theload on the engine represented by a variable such as the negativepressure in the air intake manifold or the opening of the enginethrottle valve.

2. Description of the Prior Art Attempts have been already made tocontrol the pressure of fluid supplied to multiple disc clutch means andbrake band means of fluid controlled automatic transmissions forvehicles depending on the running condition of the vehicle so as toeffectively carry out an automatic speed change, but these attempts havebeen unsatisfactory in that accurate control cannot be attained. Thepresent invention intends to simply and accurately carry out the desiredcontrol by a unique combination of electrical and hydraulic controlmeans.

The present invention provides improvements over an invention disclosedin a co-pending application Ser. No. 884,476 filed on Dec. 12, 1969entitled Hydraulic Control System for Fluid Controlled AutomaticTransmission." In the co-pending application, the inventors applied fora patent on a hydraulic control system in which the pressure regulatingaction of a pressure regulator valve is varied depending on the positionof a 1-2 shift valve element so that, when, for example, the speed ratiois changed from the first to second speed due to the operation of thel-2 shift valve element, the line pressure P in the second speed islower than the line pressure P in the first speed. This manner ofcontrol is advantageous in that it eliminates the need for the provisionof valve means including a compensator valve and a throttle relay valvewhich were employed for varying the hydraulic control operation of thepressure regulator valve and provides a very compact hydraulic actuatingcircuit. However, the proposed hydraulic control system isdisadvantageous in that a shock is developed when the manual valve ismanually shifted, for example, from the neutral range position to thedrive range position or from the neutral range position to the reverserange position. Further, a large shock takes place when the drivingpower is turned off or an upshift occurs both in a low speed range. Alarge shock also takes place during an automatic shift from the secondto first speed in the L (low range) position of the manual valve.

SUMMARY OF THE INVENTION With a view to eliminating the abovedisadvantage, it is a primary object of the present invention to providean improved hydraulic control system for a fluid controlled automatictransmission for a vehicle in which the pressure regulator valve iscontrolled by a unique combination of electrical and hydraulic controlmeans depending on the load on the engine such as the negative pressurein the air intake manifold or the opening of the engine throttle valve.

In accordance with the present invention, there is provided, in anautomatic transmission of a fluid controlled type for a vehicle having ahydraulic'torque converter, a gear unit, brake band means and clutchmeans, and fluid pressure operated servo means for said brake band meansand clutch means, a hydraulic control system comprising a pressureregulator valve means for controlling fluid pressure applied to saidfluid pressure operated servo means, means for detecting the load on theengine and generating an electrical signal depending on the load on theengine, a solenoid operated valve means for controlling fluid pressurein a valve chamber of said pressure regulator valve means, and anelectrical circuit for controlling the operation of said solenoidoperated valve means in response to the electrical signal generated bysaid electrical signal generating means, said solenoid operated valvemeans being closed and opened in response to the appearance anddisappearance of the electrical signal generated depending on the loadon the engine so as to vary the fluid pressure in the valve chamber ofsaid pressure regulator valve means thereby controlling the fluidpressure applied to said fluid pressure operated servo means. By virtueof the above arrangement, the line pressure P applied to the fluidpressure operated servo means can be most effectively controlled,depending on the running condition of the vehicle. Thus, the presentinvention eliminates an undesirable large shock that tends to developduring an automatic shift in the speed ratio as well as an excessivelylarge power loss which may occur in the oil pump due to an excessivelyhigh fluid pressure and prevents an unusual slip occurring in the brakeband means and clutch means due to an insufficient fluid pressure.

The above and other objects, features and advantages of the presentinvention will be apparent from the following detailed description ofpreferred embodiments thereof taken in conjunction with the accompanyingdrawings.

A BRIEF DESCRIPTIONOF THE DRAWINGS FIG. 1 is a schematic sectional viewof an automatic transmission to which the present invention is applied.

FIG. 2 is an enlarged sectional view taken on the line AA in FIG. 1 withparts cut away to show in detail the relation between an idler gear (notshown) in FIG. 1 and the sun gear and planet pinion.

FIGS. 3 to 8 are diagrammatic views illustrating the operating state ofa hydraulic actuating circuit according to the present invention atvarious positions, wherein FIG. 3 illustrates the operating state in theN position with a low load on the engine, FIG. 4 the operating state atthe D position lst speed with a low load on the engine, FIG. 5 theoperating state at the D position 1st speed with ahigh load on theengine, FIG. 6 the operating state at the D position 2nd speed, FIG. 7the operating state at the D position 3rd speed, and FIG. 8 theoperating state at the R position with a low load on the engine.

FIG. 9 is a circuit diagram of an electrical circuit for controlling theoperation of the solenoid operated valve means.

FIG. 10 is a diagrammatic view of another embodiment of the hydraulicactuating circuit according to the present invention, illustrating theoperating state at the D position lst speed with a low load on theengine.

FIGS. 11a and 1117 are charts showing the: variation in the linepressure P controlled by the hydraulic actuating circuit relative to thenumber of revolutions of the output shaft.

FIG. 12 is a diagrammatic view showing a partial modification of thehydraulic actuating circuit in the vicinity of the pressure regulatorvalve means.

FIG. 13 is a chart showing the variation in the line pressure Pcontrolled by the modified hydraulic actuating circuit shown in FIG. 12relative to the number of revolutions of the output shaft.

FIG. 14 is a diagrammatic view showing another partial modification ofthe hydraulic actuating circuit.

FIG. is a chart showing the variation in the line pressure P controlledby the modified hydraulic actuating circuit shown in FIG. 14 relative tothe number of revolutions of the output shaft.

FIG. 16 is a diagrammatic view showing a further partial modification ofthe hydraulic actuating circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A few preferred embodiments ofthe present invention will be described with reference to the drawings.A torque converter automatic transmission having three forward speedsand one reverse speed as shown in FIG. 1 will be taken as a typicalexample of the automatic transmission. In FIG. 1, the structure of sucha fluid controlled automatic transmission is schematically shown.

A torque converter unit includes a pump impeller 2 directly connected toa crankshaft 1 of an engine. The power developed by the engine istransmitted from the pump impeller 2 to a turbine impeller 3 through themedium of a hydraulic fluid which, is returned to enter the pumpimpeller 2 again by being guided by a stator 4. A rotational force canbe continuously derived from a turbine shaft 5 by the repetition of theabove flow of the fluid. This rotational force is transmitted from theturbine shaft 5 to a gear unit disposed at the output side of :thetorque converter unit. As is commonly known, multiple disc clutch means6 and 7 and brake band means 21 and 22 are automatically controlled byfluid pressure supplied from associated servo means as required andcooperate with a planetary gear mechanism to provide three forwardspeeds and one reverse speed.

The structure of the gear unit disposed at the output side of the torqueconverter unit will now be described. The turbine impeller 3 isconnected to the turbine shaft 5 which acts as a power input shaft ofthe planetary gear mechanism. The turbine shaft 5 is splined to a drum24 for unitary rotation therewith. Disposed within the drum 24 is amultiple 1 disc clutch 6 (hereinafter to be referred to as a frontclutch) which is engaged by means of a piston 25 actuated by fluidpressure and is released by means of back-up springs. The drive platesof the front clutch 6 are externally splined to engage the internallysplined portion of the drum 24, and the clutch discs are internallysplined to engage the externally splined portion of a hub 26 so as to belocked against free rotation. The hub 26 is internally splined to engagethe externally splined portion of an intermediate shaft 8. The clutcbdiscs of a multiple disc clutch 7 (hereinafter to be referred to as arear clutch) are internally splined to engage the externally splinedportion of the front clutch drum 24 as shown so as to be locked againstfree rotation. Thus, the clutch discs of the rear clutch 7 rotate inunison with the front clutch drum 24. The driven plates of the rearclutch 7 are externally splined to engage the internally splined portionof a clutch drum 27 of the rear clutch 7. The rear clutch 7 is engagedby means of a fluid pressure actuated piston 28 and disengaged when thefluid pressure applied to the piston 28 is released.

The intermediate shaft 8 which is splined to the hub 26 of the frontclutch 6 is connected at its rear end to an input sun gear 9. The rearclutch drum 27 is fixed to a reverse sun gear 20 by a suitable lockingmeans. The input sun gear 9 meshes with each gear 12 of a plurality of,for example, two or three planet pinions 11. The reverse sun gear 10meshes with idler gears 15 (shown in FIG. 2) which are each rotatablymounted on a pin 14 fixed at one end to a carrier 13, and the idlergears 15 in turn mesh with gears 16 of the planet pinions 11.

The rearmost gear 17 of each planet pinion ll meshes with a gear 19mounted at the front end of an output shaft 18 of the transmission. Theplanet pinions 11 having the gears 16, 12 and 17 and the idler gears orpinions 15 are carried by the carrier 13 by means of pinion pins 20 and14 respectively. A brake band 21 (hereinafter to be referred to as arear brake band) encircles the carrier 13 for applying a brake to thelatter, and thus the carrier 13 can be fixed against rotation andallowed to freely rotate by fastening and releasing the rear brake band21. Similarly, a brake band 22 (hereinafter to be referred to as a frontbrake band) encircles the rear clutch drum 27 so that the rear clutchdrum 27, hence the reverse sun gear 10 can be fixed against rotation andallowed to freely rotate by fastening and releasing the front brake band22. A one-way clutch 23 associated with the carrier 13 functions in amanner similar to the rear brake band 21 in low gear set forthhereunder.

With the above structure, three forward speeds and one reverse speed canbe obtained by selectively actuating the elements described above in themanner described as follows:

First speed The front clutch 6 and the rear brake band 21 are actuated.(However, when the transmission is driven from the engine, the rearbrake band 21 may not be actuated since the one-way clutch 23 isactuated to give the same result as that obtained with the actuation ofthe rear brake band 21. In this case, however, no driving force istransmitted from the output shaft 18.) With the front clutch 6 and therear brake band 21 so actuated, the rotation of the turbine shaft 5 isdirectly transmitted to the input sun gear 9 through the front clutch 6.Due to the face that the carrier 13 is locked against rotation by therear brake band 21, the pinion pins 20 are also held stationary and therotation of the turbine shaft 5 is transmitted from the gear 9 to thegears 12, thence through the gears 17 to the gear 19 mounted on theoutput shaft 18 in a speed reducing relation similar to that of anordinary gear train, thereby providing the first speed.

Second speed The front clutch 6 is kept actuated and the front brakeband 22 is actuated while releasing the gear brake band 21. Thus, theinput sun gear 9 is rotated in unison with the turbine shaft 5, but therear clutch drum 27, hence the reverse sun gear is locked againstrotation by the front brake band 22. In this state, the rotation of theturbine shaft 5 is directly transmitted to the input sun gear 9, and thesun gear 9 urges the pinions 11 to rotate in a direction(counterclockwise) opposite to the direction of rotation (clockwise) ofthe turbine shaft 5. The planet pinions 11 rotating in this directiontry to rotate the idler gears clockwise through the gears 16. However,due to the fact that the gear 10 meshing with the gears 15 is lockedagainst rotation, the pinion pins 14 revolve clockwise around the gear10. This revolving motion is imparted to the rotation of the input sungear 9 and the gear 19 carried by the output shaft-18 which gears arecoaxial with and rotate in the same direction as the turbine shaft 5.Since the number of teeth of the gear 12 is selected to be greater thanthe number of teeth of the gear 17, the number of revolutions of theintermediate shaft 8 is greater than that of the output shaft 18. Inother words, the output shaft 18 is rotated at a reduced speed or secondspeed.

Third speed The third speed can be obtained by engaging both the frontand rear clutches 6 and 7. The

' input sun gear 9 and the reverse sun gear 10 are rotated in unison andthe whole planetary gear system is unitarily rotated so that the outputshaft 18 is rotated at the rotating speed of the turbine shaft 5.

Reverse When reversing, the rear clutch 7 and the rear brake band 21 areactuated. The carrier 13, hence the pinion-pins 14 and are therebylocked against revolution, and the rotation of the turbine shaft 5 istransmitted through the rear clutch 7 to the reverse sun gear 10, thencethrough the pinions 15 and 17 to the gear 19 mounted on the output shaft18 so that the output shaft 18 is rotated in the reverse direction.

A hydraulic actuating system for supplying and discharging fluid underpressure to and from the brake bands 21 and 22 and the clutches 6 and 7in the automatic transmission for carrying out an automatic shift willnext be described. The arrangement of one form of the hydraulicactuating system according to the present invention is diagrammaticallyshown in FIGS. 3 to 8. Briefly, the hydraulic actuating system comprisesa fluid pressure source 100 and a hydraulic actuating circuit 1 10. Thehydraulic actuating circuit 110 includes a manual valve 120, a l-2 shiftmeans 130, a 2-3 shift means 135, a first check valve 140 and fluidpassages. The fluid pressure source 100 includes an oil pump 101, an oilstrainer 102, a pressure regulator valve 105, a solenoid operated valvemeans 150, a second check valve 103, an oil cooler 104, a third checkvalve 107 and fluid passages. The fluid pressure source 100 functions tosupply fluid under pressure to the torque converter, to the gears forlubricating same and to the hydraulic actuating circuit 110.

The manual valve 120 is connected with a shift lever (not shown)disposed adjacent to the drivers seat and takes one of the sixpositions, that is, the P (parking range), R (reverse range), N (neutralrange), D (drive range), 2 (second range) and L (low range) positions.When now the manual valve 120 takes the N position, a fluid passage 121is closed and valve chambers 122 and 123 are exhausted as seen in FIG.3. At the D position of the manual valve 120, the fluid passage 121communicates with fluid passages 124, and 126 as seen in FIGS. 4 to 7.The fluid passage 124 leads directly to a front clutch servo chamber 6a,and the fluid passage 125 leads to the apply side 22a of a servo for thefront brake band 22 through the l-2 shift means 130, while the fluidpassage 126 leads to a rear clutch servo chamber 7a and to the releaseside 22b of the servo for the front brake band 22 through the 2-3 shiftmeans 135 and the check valve 140. The 1-2 shift means 130 includes al-2 shift valve element 131 and a solenoid 132. One end (or theright-hand end as viewed in the drawing) of the valve element 131 isabutted by a moving core 133 of the solenoid 132. When no current issupplied to the solenoid 132, the valve element 131 is urged to itsrightward position by a spring 131 engaging the other'or left-hand endof the valve element 131 so that the fluid passage 125 communicates witha fluid passage 134 to supply fluid to the apply side 22a of the servofor the front brake band 22 to apply the front brake band 22. Whencurrent is supplied to the solenoid 132, the moving core 133 urges thevalve element 131 to the leftward position by being actuated by theelectromagnetic force of the solenoid 132 so that the communicationbetween the fluid passages 125 and 134 is interrupted and the fluidpassage 134 communicates with a pressure discharge port 134a to releasethe front brake band 22. Similarly, the 2-3 shift means 135 includes a2-3 shift valve element 136 and a solenoid 137. One end (or theright-hand end as viewed in the drawing) of the valve element 136 isengaged by a moving core 138 of the solenoid 137. When no current issupplied to the solenoid 137, the valve element 136 is urged to itsrightward position by a spring 136 engaging the other or left-hand endof the valve element 136 so that the fluid passage 126 communicates witha fluid passage 139 to force a check ball element 141 of the check valvetoward a fluid passage 128 to block the fluid passage 128. As a result,the fluid passage 139 communicates with a fluid passage 142 to supplyfluid to the rear clutch servo chamber 7a and to the release side 22b ofthe servo for the front brake band 22 so as to engage the rear clutch 7and release the front brake band 22. When current is supplied to thesolenoid 137, the valve element 136 is urged leftward so that thecommunication between the fluid passages 126 and 139 is interrupted andthe fluid passage 139 communicates with a pressure discharge port 139ato be exhausted.

In the first speed at the drive rangeposition or D position 1st speedshown in FIGS. 4 and 5, both the solenoids 132 and 137 are energized andthe front clutch 6 is solely engaged by the supply of 'fluid from themanual valve 120 to the front clutch servo chamber 6a through the fluidpassage 124. Accordingly, when the transmission is driven from theengine, the one-way clutch 23 is engaged to lock the carrier 13 againstrotation so that the first speed can be obtained. In this case, however,no driving force can be transmitted from the output shaft 18 since afreewheeling condition appears.

In the second speed at the drive range position or D position 2nd speedshown in FIG. 6, the fluid passage 124 leading to the front clutch servochamber 6a is kept pressurized and the solenoid 132 for the 1-2 shiftvalve element 131 is de-energized with the result that the fluid passage125 communicates with the fluid passage 134 to supply fluid to the applyside 22a of the servo for the front brake band 22 to apply the frontbrake band 22. Thus, the second speed can be obtained.

in the third speed at the drive range position or D position 3rd speedshown in FIG. 7, the solenoid 137 for the 23 shift valve element 136 isde-energized in addition to the previous de-energization of the solenoid132 in the D position 2nd speed with the result that the fluid passage126 communicates with the fluid passage 139 to supply fluid to the rearclutch servo chamber 7a to engage the rear clutch 7 while releasing thefront brake band 22. Thus, the third speed can be obtained.

When the manual valve 120 is urged to the 2 position, the fluid passage126 leading to the 2-3 shift means 135 is exhausted and the fluidpassages 124 and 12S communicate solely with the fluid pressure source100. Accordingly, it is impossible to obtain the third speed regardlessof the de-energization of the solenoid 137 for the 2-3 shift valveelement 136 and the first and second speeds can be obtained depending onthe energization and deenergization of the solenoid 132 for the l-2shift valve element 131.

When the manual valve 120 is urged to the L position, the fluid passages125 and 126 are exhausted and the fluid passages 124 and 127 communicatewith the fluid pressure source 100. As a result, fluid is supplied tothe front clutch servo chamber 6a and to the apply side 21a of a servofor the rear brake band 21 to engage the front clutch 6 and apply therear brake band 21. Thus, the first speed can be obtained. The firstspeed in this case differs from the first speed in the D position inthat the rear brake band 21 is applied to provide for transmission ofthe driving force from the output shaft 18 to the engine therebypermitting the application of engine braking.

When the manual valve 120 is moved to the R position shown in FIG. 8,the fluid passages 124i, 125 and 126 are exhausted and the fluidpassages 127 and 128 communicate with the fluid pressure source 100. Asa result, fluid is supplied to the rear clutch servo chamber 7a and tothe apply side 21a of the servo for the rear brake band 21 to engage therear clutch 7 and apply the rear brake band 21. Thus, the reversedriving condition for the vehicle can be obtained.

It will be understood from the above description that the l-2 shiftmeans 130 and the 2-3 shift means 135 are operated to carry out theautomatic speed changing operation and this is accomplished byselectively energizing and de-energizing the solenoids 132 and 137. Theshift control by supplying current and interrupting the supply ofcurrent to the solenoids 132 and 137 is carried out depending on therunning condition of the vehicle, and various methods for the shiftcontrol have been proposed heretofore and are well known in the art. Forexample, U.S. Pats. Nos. 3,068,7l and FIG. 10 shows diagrammaticallyanother embodiment of the present invention and like reference numeralsare used therein to denote like parts appearing in FIGS. 3 to 8. Whilethe preceding embodiment has referred to the case in which the solenoids132 and 137 associated with the respective shift valve elements 131 and136 are selectively energized and de-energized for the electrical shiftcontrol, the embodiment shown in FIG. 10 relates to a system in whichthese shift valve elements are selectively hydraulically actuated byfluid pressure depending on the running condition of the vehicle as isthe case with conventional control systems.

Referring to FIG. 10, a governor pressure P, responsive to the vehiclespeed is produced at a governor valve 201 and is applied by way of afluid passage 202 to fluid chambers adjacent to one end of a l-2 shiftvalve element 131 and a 2-3 shift valve element 136. On the other hand,a throttle pressure P responsive to the position of the engine throttlevalve is produced at a throttle valve 203 operatively connected with theengine throttle valve. Therefore, a pressure responsive to the positionof the accelerator pedal is applied by way of fluid passages 204 and 205to fluid chambers adjacent to the other end of the l-2 shift valveelement 131 and the 2-3 shift valve element 136. Thus, the governorpressure P and the throttle pressure P are applied to the fluid chambersadjacent to the opposite ends of the 1-2 shift valve element 131 and the2-3 shift valve element 136 to move these valve elements in eitherdirection depending on the relation between the vehicle speed and theposition of the engine throttle valve. While FIG. 10 shows the operatingstate of the hydraulic actuating circuit at the D position lst speed, itis apparent that a manual valve 120 can take any one of the P, R, N, D,2 and L positions and the hydraulic actuating circuit can operate in amanner similar to that described in the preceding embodiment. In thehydraulic actuating circuit shown in FIG. 10, the throttle pressure Pappearing in the fluid passage is modulated or reduced by a valve 106into a modulated throttle pressure P of constant magnitude and thismodulated throttle pressure P appears in a fluid passage 207 to beapplied to the corresponding end of the shift valve elements 131 and136.

The fluid pressure or line pressure P applied to the servos for thebrake bands and multiple disc clutches for carrying out the speedchanging operation is controlled by the pressure regulator valve 105.The present invention is featured by controlling the line pressure P,,by means of the pressure regulator valve 105 so as to obtain a fluidpressure characteristic as shown in FIGS. 1 1a and 11b.

The structure and operation of the pressure regulator valve 105 which isan important feature of the present invention will be described withreference to FIGS. 3 to 8, and more especially to FIGS. 4 to 6. Thepressure regulator valve 105 comprises a valve body 91, a valve spool105', a coil spring 106 compressed between one or upper end of the valvespool 105 and the valve body 91, and six fluid chambers 108, 115, 111,112, 109 and 113 arranged in this order from above. The fluid chamber112 communicates with a pressure discharge port 114 for returning fluidto the oil reservoir. When the valve spool 105' of the pressureregulator valve 105 is in its upper position, the fluid chamber 112communicates with the fluid chamber 111 to discharge a controlled amountof fluid from the fluid chamber 111 to the oil reservoir. The fluidchamber 111 is connected to the fluid chamber 108 by a fluid passage121'. The fluid chamber 111 is further connected to the fluid passage121 which supplies fluid under pressure pumped up by the oil pump 101.When the valve spool 105 is in its upper position, the fluid chamber 115supplies fluid into a fluid circulating passage 99 leading to the torqueconverter. The fluid chamber 109 is connected to the third check valve107 having a check ball element 156 therein, thence to the fluidpassages 134 and 151. The fluid chamber 113 is always exhausted.

The line pressure P regulated by the pressure regulator valve 105, thatis, the fluid pressure supplied from the fluid chamber 111 into thefluid passage 121 is determined by the combination of the downward forceF of the coil spring 106 disposed between the upper end of the valvespool 105 and the valve body 91, the fluid pressure P in the fluidchamber 108 acting upwardly on the valve spool 105', and the fluidpressure P in the fluid chamber 109 acting upwardly on the valve spool105. Suppose that AA is the difference between the cross-sectional areasof the portion of the valve spool 105' fitting in the fluid chamber 108,and AA is the difference between the cross-sectional areas of theportion of the valve spool 105' fitting in the fluid chamber 109. Then,the following equation holds:

Since the fluid chamber 108 communicates with the fluid chamber 111 bythe fluid passage 121', the following equation holds:

1= 2 2) The fluid pressure P in the fluid chamber 109 will now beconsidered. The fluid chamber 109 is connected to the I2 shift means 130through the fluid passage 134', the third check valve 107 and the fluidpassage 134. The fluid passage 134 supplies the fluid pressure appearingin the fluid passage 125 to the apply side 22a of the servo for thefront brake band 22 in response to the actuation of the shift valveelement 131 of the l-2 shift means 130 by the solenoid 132. When the l-2shift valve element 131 is thus actuated to provide the second speed,fluid under line pressure P is supplied into the fluid chamber 109 byway of the fluid passages 134 and 134. Conversely, in the first speedposition of the hydraulic actuating circuit, the fluid passage 134 isexhausted through the pressure discharge port 134a and therefore thefluid chamber 109 is also exhausted. In the third speed position of thehydraulic actuating circuit, the 1-2 shift means 130 remains in the samestate as when the hydraulic actuating circuit is in the second speedposition, and fluid under line pressure P is supplied into the fluidchamber 109 as in the case of the second speed.

The fluid chamber 109 is connected through the fluid passage 134 and thethird check valve 107 to the fluid passage 151. The fluid passage 151 isdivided into two branch passages one of which leads to the fluid chamber111 through an orifice 158 and the fluid passage 121', while the otherleads to the solenoid operated valve means 150. The solenoid operatedvalve means 150 comprises a valve element 152, a solenoid 153, adischarge port 154 operatively closed by the valve element 152, and aspring' l55 normally urging the valve element 152 upwardly. Current issupplied to the solenoid 153 in a manner as will be described later whenthe load on the engine is low, and thus the valve element 152 is forceddownwardly to close the discharge port 154. In this case, the fluidpressure in the fluid passage 151 is equal to the fluid pressure in thefluid chamber'lll. That is, the fluid pressure in the fluid passage 151is equal to the line pressure P Therefore, the fluid pressure P in'thefluid chamber 109 is also equal to the line pressure P The solenoid 153is de-energized when the load on the engine is high. Therefore, thevalve element 152 is forced upwardly by the combined action of the fluidpressure and the force of the spring 155 so that fluid isdischargedthrough the discharge port 154. The discharge'port 154 has anarea which is sufficiently larger than the flow limiting area of theorifice 158 so as to release the fluid pressure in the fluid passage151. Therefore, the fluid pressure P in the fluid chamber 109 is zero inthe high engine load range except in the second and third speed, thatis, except the case in which the check ball element 156 of the thirdcheck valve 107 is forced leftward to block the fluid passage 151. Fromthe above explanation, it is apparent that the line pressure P when P 0and P F is given by the following Equations (3) and (4) respectively:

PL: (F)/( A1+ 2) (4) It will be seen that the line pressure P has ahigher constant value when the fluid pressure P does not exist in thefluid chamber 109 than when the fluid pressure P exists in the fluidchamber 109. The magnitude of the line pressure P relative to theposition of the manual valve is summarized in Table 1.

TABLE 1 Position of manual Engine Load Line valve Speed pressure HighF/AA lst speed Low F/(AA +AA D range 2nd speed No relation with loadF/(AA, AA,) 3rd speed No relation with load F/(AA AA High FIAA lst speed2nd Low F/(AA, AA,) range 2nd speed No relation with load F/(AA, AA,) Land High F/AA R ranges Low F/(AA, AAz) High F/AA N range Low FIGS. 11aand 11b are charts showing the line pressure P shown in Table 1. InFIGS. 11a and 11b, it is defined that the load on the engine is highwhen the opening of the throttle valve is more than 0.5/4, while theload on the engine is low when the opening of the throttle valve is lessthan 0.5/4. The line pressure P F/AA, corresponding to P O is 10 kg/cm,while the line pressure P FHA/11+ AA corresponding to P P is 5 kglcmFIG. 11a shows the line pressure P when the position of the manual valve120 is in the L, R and N ranges, while FIG. 11b shows the line pressureP when the position of the manual valve 120 is in the D and 2 ranges. Itwill be seen from FIG. 11a that, in the L, R and N ranges, the 1-2 shiftmeans 130 is not actuated, the fluid passage 134 is kept exhausted andthe check ball element 156 of the third check valve 107 is in itsrightward position to allow for communication between the fluidpassages'134' and 151 so that the fluid pressure in the fluid chamber109 of the pressure regulator valve 105 is controlled solely by thesolenoid operated valve means 150. Since the solenoid operated valvemeans 150 is energized or de-energized depending on the load on theengine, the line pressure P is represented by two lines which are notsubject to any change and are independent of the vehicle speed as seenin FlG. 11a. More precisely, the line pressure P is continuously kept atkg/cm when the load on the engine is high due to the large opening ofthe engine throttle valve of more than 0.5/4, while the line pressure Pis continuously kept at S ltglcm when the load on the engine is low dueto the small opening of the engine throttle valve of less than 0.5/4.

In the case of the D or 2 range shown in FIG. 11b, the operation of thel2 shift means 130 is added to the operation of the above means. Supposethat the fluid pressure P in the fluid chamber 109 of the pressureregulator valve 105 is zero when the load on the engine is high due tothe large opening of the engine throttle valve of more than 0.5/4. Whenthe speed ratio is changed from the first to second speed due to thedeenergization of the solenoid 132 of the l2 shift means 130, fluidunder line pressure P is supplied from the fluid passage 125 to thefluid passage 134. The check ball element 156 of the third check valve107 is forced to its leftward position by the line pressure P,, so thatthe fluid under line pressure P is supplied through the fluid passage134 into the fluid chamber 109 of the pressure regulator valve 105. Thisis the same as when the load on the engine is low in the L, R and Nranges due to the small opening of the engine throttle valve of lessthan 0.514, and thus the line pressure P steps down from l0 kg/cm to 5kg/cm as seen in FIG. 11b. When the load on the engine is low in the Dand 2 ranges due to the small opening of the engine throttle valve ofless than 0.5/ 4, the line pressure P is continuously kept at 5 kg/cmand is not subject to any change at any vehicle speed.

it will be seen that the line pressure P steps down from a constant highpressure to a constant low pressure in response to the de-energizationof the solenoid 132 of the l2 shift means 130 when the load on theengine in the D or 2 range is high due to the large open ing of theengine throttle valve of more than 0.514. However, the l2 shift point isgenerally variable depending on an engine torque responsive signal.Thus, the point at which the step-down occurs from the constant highpressure to the constant low pressure varies depending on the enginetorque responsive signal. The step-down occurs earlier with a smalleropening of the engine throttle valve and is gradually retarded with theincrease in the opening of the engine throttle valve. A

fluid pressure control similar to that described above is also carriedout in another embodiment of the present invention is shown in FIG. 10.

The fluid pressure regulating action of the pressure regulator valve issuch that a controlled amount of fluid is discharged from the fluidchamber 111 into the fluid chamber 112, thence into the discharge port114 depending on the fluid pressure in the fluid chamber 108. That is,the manner of fluid pressure control is such that the fluid flow betweenthe fluid chambers 111 and 112 is limited to a very small amount or iscompletely shut off to quickly raise the fluid pressure in the fluidchamber 108 when an insufficient fluid pressure exists in the fluidchamber 108, while the fluid flow between the fluid chambers 111 and 112is increased to discharge a large amount of fluid from the fluid chamber111 to the fluid chamber 112 when an excessively large fluid pressureexists in the fluid chamber 108. The change-over between the two linepressure levels by the operation of the l2 shift means 130 only occursin the D or 2 position of the manual valve in which fluid under pressureis supplied to the fluid passage leading to the l2 shift valve element131. In the N or R position of the manual valve 120, no fluid issupplied to the 1-2 shift means 130. Therefore, the l2 shift means doesnot participate in the change-over between the two line pressure levels,and the change-over is effected by the operation of the solenoidoperated valve means 150. in the event of trouble in the electricalcircuit, no current is supplied to the solenoid 153 of the solenoidoperated valve means 150. It is another important feature of the presentinvention that, in this instance, the valve element 152 is urgedupwardly by the force of the spring 155 to discharge fluid out of thefluid chamber 109 so that the line pressure P has a relatively highvalue thereby providing for safe operation of the system.

Generally, the number of revolutions of the oil pump is low in theidling state of the engine so that the line pressure P may be reduced inthe idling state and the amount of fluid supplied to the line 99 leadingto the torque converter may be reduced. Thus, it is undesirable todischarge fluid from the solenoid operated valve means 150. However, thepresent invention is free from such trouble because the valve element152 of the solenoid operated valve means is in its closed position inthe idling state of the engine.

As described above, the solenoid operated valve means 150 is providedfor the purpose of controlling the line pressure P produced by thepressure regulator valve 105. One form of an electrical circuit forenergizing the solenoid operated valve means 150 depending on the loadon the engine will be described with reference to FIG. 9. The electricalcircuit includes a switch 501 such as, for example, a reed switch whichis urged to the closed position when the opening of the engine throttlevalve exceeds 0.5/4, a pair of transistors 502 and 503 acting as asemiconductor relay, a coil 504 of the solenoid operated valve means150, a diode 507 for absorbing the counter-electromotive force producedin the coil 504 thereby protecting the transistor 503 against damage,positive terminals 505 and 506 of a power supply, and resistors 508-513.In operation, when the opening of the engine throttle valve is less than0.514 or the engine throttle valve is

1. In a fluid controlled type automatic transmission for vehiclesincluding a hydraulic torque converter or hydraulic coupling, a gearunit having brake band means and clutch means, fluid pressure operatedservo means for said brake band means and said clutch means, a source offluid pressure, a fluid pressure circuit for supplying and dischargingfluid under pressure to and from said servo means, said circuitincluding shift valve means responsive to a predetermined runningcondition of the vehicle for establishing low speed and high speedforward drive ratios for said gear unit, and a pressure regulator valvefor controlling the fluid pressure delivered from said source to saidfluid pressure circuit, said regulator valve including a valve spool anda plurality of valve chambers, the improvement comprising control meansfor varying the pressure regulating action of said regulating valve inaccordance with engine load, said means including a control valve influid connection with one of said valve chambers for controlling fluidpressure in said chamber and means responsive to engine load for openingand closing said control valve to thereby effect movement of thepressure regulator valve spool.
 2. Apparatus as in claim 1 wherein saidregulator valve is responsive to the operation of said control valve ina mode to deliver low and high fluid pressure to said fluid pressurecircuit when engine load is low and high, respectively.
 3. Apparatus asin claim 1 wherein said means responsive to engine load generates anelectrical signal depending on engine load, wherein said control valveis a solenoid operated valve adapted to be closed and opened in responseto the appearance and disappearance, respectively, of said electricalsignal, and wherein the pressure delivered from said pressure regulatorvalve to said fluid pressure circuit is high when no electrical signalis applied to said solenOid valve.
 4. Apparatus as in claim 1 whereinsaid control means for varying the pressure regulating action of saidregulating valve is also responsive to operation of said shift valvemeans, said control means including fluid passage means extendingbetween said shift valve means and said one valve chamber in saidpressure regulator valve for changing the pressure in said valve chamberupon a preselected operation of said shift valve means.
 5. In a fluidcontrolled type automatic transmission for vehicles including ahydraulic torque converter or hydraulic coupling, a gear unit havingbrake band means and clutch means, fluid pressure operated servo meansfor said brake band means and said clutch means, a source of fluidpressure, a fluid pressure circuit for supplying and discharging fluidunder pressure to and from said servo means, said circuit includingshift valve means responsive to a predetermined running condition of thevehicle for establishing low speed and high speed forward drive ratiosfor said gear unit, and a pressure regulator valve for controlling thefluid pressure delivered from said source to said fluid pressurecircuit, said regulator valve including a valve spool and a controlchamber containing fluid acting on said spool, the improvementcomprising: means defining a control chamber containing fluid acting onsaid pressure regulator valve spool, said pressure regulator valve beingconstructed such that movement of said spool under increased pressure insaid control chamber decreases the fluid pressure delivered to saidfluid pressure circuit by said pressure regulator valve; a solenoidoperated valve in fluid connection with said control chamber and havinga discharge port and movable valve element for selectively closing saidport and opening said port to place the same in fluid communication withsaid control chamber, said solenoid operated valve being closed whenelectrically energized and being open when de-energized; means fordetecting the load on the engine and for generating an electrical signalwhen the load exceeds a predetermined value; and an electrical circuitfor controlling said solenoid operated valve in response to theelectrical signal generated by said electrical signal generating means.6. Apparatus as in claim 5 including fluid passage means extendingbetween said shift valve means and said control chamber in said pressureregulator valve for introducing fluid pressure from said shift valvemeans into said control chamber upon a preselected operation of saidshift valve means and for preventing discharge of said introduced fluidpressure through said solenoid operated valve should the latter be inthe open position.